A House committee is investigating last month's attack that killed the ambassador to Libya and three other Americans at a consulate in the city of Benghazi. And today, senior State Department officials will be on the receiving end of politically-charged questions. Republicans say that the Obama administration rejected repeated requests for more security.

NPR's Michele Kelemen has more.

MICHELE KELEMEN, BYLINE: A Republican on the House Oversight Committee, Jason Chaffetz, traveled to Libya over the weekend to prepare for today's hearing and he has lots of questions about why requests for more security were denied.

REPRESENTATIVE JASON CHAFFETZ: Remember, Libya is a situation that just went through a revolution. Our compound in Benghazi had been bombed twice. And right around corner at the British consulate there in Benghazi, the British ambassador had experienced two assassination attempts. So this is a very tumultuous situation in the run-up to 9/11.

KELEMEN: Among the witnesses Republicans called are Eric Nordstrom, who was a State Department regional security officer in Libya and Lieutenant Colonel Andrew Wood, who headed a security support team there. Chaffetz says they will lay out the requests they made for more resources and the responses they got from Washington.

CHAFFETZ: At least one, if not both of these gentlemen, will testify they were told: Don't put that in writing anymore. You are not going to get it. Don't ask for it. Don't do that.

KELEMEN: Colonel Wood told CBS News that Ambassador Chris Stevens, who was killed in Benghazi, was constantly concerned about the threats to himself and the entire staff there and Wood wanted his team to stay beyond August.

The State Department says the departure of that security support team had no impact on the total number of fully trained American security personnel in Libya. And points out that the team was based in Tripoli, not Benghazi.

At her daily briefings, State Department spokesperson Victoria Nuland has been tight lipped about such details, saying only the department is cooperating with members of congress.

VICTORIA NULAND: We consider the Hill a vital partner in our efforts to ensure that our diplomats and our facilities are secure. So we are doing as much as we can to be responsive to the various requests that we've had.

KELEMEN: Utah Congressman Chaffetz accuses the administration of downplaying the terrorist threat in Libya, to try to make things look more normal.

CHAFFETZ: Rather than security dictating security, they wanted the political talking point to be able to show that they were, quote/unquote, "normalizing as quickly as possible."

KELEMEN: Democrats say Republicans are playing politics, withholding documents and effectively excluding Democrats from that trip to Libya over the weekend. Committee Democrats also note that since 2011, House Republicans voted to cut embassy security funding by about half a billion dollars, though the Senate restored some of that money.